JERUSALEM — Days before Secretary of State John Kerry’s return to the region, anger and defiance continued to flare across the West Bank on Thursday as Palestinians buried two teenagers killed by Israeli soldiers during protests triggered by the death of a prisoner with cancer while in Israeli custody.

Masked militiamen fired into the air at the prisoner’s funeral, in the volatile city of Hebron, where some of the thousands of mourners called for a third intifada, or uprising.

Clashes between Israeli soldiers and Palestinian youths hurling stones and firebombs erupted there and in other West Bank locations for the third straight day, as Palestinian leaders accused Israel of escalating tensions in order to thwart Washington’s efforts.

“It seems that Israel wants to spark chaos in the Palestinian territories,” President Mahmoud Abbas of the Palestinian Authority told leaders of his Fatah faction at a meeting in Ramallah. “Israel on every occasion is using lethal force against peaceful young protesters, and peaceful demonstrations are being suppressed with the power of weapons. This is not acceptable at all.”

Mr. Abbas’s spokesman, Nabil Abu Rudeineh, said in a statement, “This escalation proves that the Israeli government only looks at reality through brute power, settlement activities, and Judaization.”

Mark Regev, a spokesman for Prime Minister Benjamin Netanyahu of Israel, said such comments, as well as previous ones asserting that Israeli negligence was to blame for the 64-year-old prisoner’s death, threatened the “serious efforts under way” since President Obama’s visit here last month to restart the stalemated peace process.

“We are concerned that there are elements in the P.A. that seem to refuse to jettison the harsh language of confrontation, and try to exploit different incidents to stir up trouble,” Mr. Regev said in an interview. “The only path to Palestinian statehood is through peace and reconciliation with Israel. Extreme confrontational language, incitement to violence, does not serve that end.”

Some analysts said the renewed violence and the second death of a prisoner in two months, made the prospect of diplomatic progress remote, with the Palestinian street increasingly restive and Mr. Abbas under pressure even from leaders of his own party to pursue claims against Israel in the International Criminal Court, a move Washington has urged him to delay. But others said the worsening situation on the ground could lend a new urgency to Mr. Kerry’s outreach.

“On the one hand it complicates the situation for Kerry, on the other hand it says something about the need to intensify American efforts,” said Ghassan Khatib, vice president of Birzeit University in the West Bank and a former Palestinian Authority spokesman. “If things will be left to local and internal dynamics, things might get out of hand.”

Shlomo Brom, director of the program on Israel-Palestinian relations at the Institute for National Security Studies at Tel Aviv University, said both sides wanted to avoid an intifada, and that the change in Israel’s cabinet and governing coalition could provide Mr. Kerry an opening.

“As a result of the recent developments,” Mr. Brom said, “I think it is easier for the two leaderships to get off the trees they climbed on.”

Unrest in the West Bank, which has been simmering for months, picked up after the death Tuesday morning of Maysara Abu Hamdiya, a retired general in the Palestinian security services who had been serving a life sentence for his involvement in a failed 2002 suicide bombing in a Jerusalem cafe. Autopsies by both Israeli and Palestinian officials confirmed that Mr. Hamdiya died of cancer, which began in the vocal cords and spread to the lungs, neck, chest, liver, spine and ribs. The Palestinians have accused the Israeli authorities of deliberately delaying his diagnosis and treatment.

The thousands of Palestinian prisoners in Israeli jails hold a hallowed place in Palestinian society, and Mr. Hamdiya was buried with military honors. His death seemed to at least temporarily unite the deeply divided Palestinians, at a huge funeral dotted with flags of Fatah and its rivals, Hamas and Islamic Jihad, and attended by dozens of masked members of Fatah’s military wing, the Al Aksa Martyrs Brigades, which has mostly lain low in recent years.

“We will not allow the Israelis to kill our people, especially the prisoners,” a spokesman for the Brigades told the crowd. “We are calling on President Abbas to give us a green light to react to what happened to Maysara Abu Hamdiya.”

A similar scene unfolded farther north near Tulkarm, where the bodies of the two teenagers fatally shot overnight — but not their bloodied faces — were covered with Palestinian flags, and mourners called for “revenge.”

The Israeli military said that the youths were hurling firebombs at an army post late Wednesday, and that soldiers responded with live fire; it is investigating the episode.

Amer Nassar, 17, was killed on the spot. The body of Naji Balbisi, 18, was found in the early hours of Thursday.

Mayor Salah al-Najeeb of Anabta, the village near Tulkarm where both young men lived, said “the soldiers opened fire to kill.” Tayyeb Abdul Rahim, a member of the Fatah Central Committee, said: “These sacrifices will only make us committed to our just national rights. We will not retreat, surrender nor give up any drop of our soil.”

Palestinian officials said 21 people were injured by rubber bullets and dozens more affected by tear gas in the clashes in Hebron, which continued into the evening.

Sabri Saidam, a leader of the Fatah Revolutionary Council, which met Thursday in Ramallah with Mr. Abbas, said many of the party leaders expressed frustration that the Palestinians’ upgraded status in the United Nations had not been used to gain access to the International Criminal Court and similar agencies.

“Obviously tension is running high and people are saying we should not give up the pressure that needs to be exerted on Israel,” Mr. Saidam said of the growing protests in the West Bank. “But the main talk is focusing on diplomatic channels and international channels through our membership in the U.N.”

Aaron David Miller, a longtime peace negotiator who is now vice president of the Woodrow Wilson International Center for Scholars in Washington, said this week’s deterioration did not bode well for Mr. Kerry’s visit.

“We are way, way beyond the point where this process will be able to survive the terror and the violence and the intimidating tactics that both sides use in an attempt to influence the negotiations,” Mr. Miller said. “If this is truly going to work, then the out-of-the-negotiating-room environment, what Israelis and Palestinians are doing to each other on a daily basis, has to reach a point of general tranquillity.”

Khaled Abu Aker contributed reporting from Ramallah, West Bank, and Nayef Hashlamoun from Hebron, West Bank.

A version of this article appears in print on , Section A, Page 8 of the New York edition with the headline: Palestinian Defiance on Display at West Bank Funerals. Order Reprints | Today’s Paper | Subscribe